In the film, Carlotta is Prince Eric's maid and one of his most loyal friends. When Eric brings Ariel into his castle, she gives her a bath and has her dress washed for her. Then she dresses her up all nicely and takes her to the dining room where she will eat with Eric and Grimsby.
When Ariel takes Grimsby's pipe and blows its contents in his face, both Eric and Carlotta laugh about it, and Carlotta tells Eric that that's the first time she's seen him smile in weeks. Grimsby then asks her what's for dinner to which she answers that he's going to love it because Chef Louis has been making them stuffed crab. When they hear a noise from the kitchen, Carlotta decides to go and see what Chef Louis is up to.
When she reaches the kitchen she finds him throwing stuff around and making a mess. She furiously asks him what he's doing to which he apologizes to her for making such a mess. She then takes the food back to the table for Eric, Grimsby, and Ariel. The next day she and Grimsby are seen waving goodbye to Eric and Ariel as they leave to take a tour of the kingdom. She is finally seen again at the end of the film at Ariel and Eric's wedding to where she becomes overly emotional and cries in Grimsby's shirt.
Carlotta appears again in the sequel but has a smaller role than in the previous film. She is first seen singing "Down to the Sea" and celebrating the arrival of Melody. Then, when the party gets interrupted by Ursula's sister, Morgana, she moves away from her, frightened.
Carlotta is seen 12 years later cleaning up for Melody's twelfth birthday party. When Ariel asks her if she's seen Melody, she replies, "Not since this morning, Your Majesty". When Chef Louis ruins Melody's party by chasing after Sebastian and making everyone laugh, Carlotta splashes him with a bucket of water and says, "Oh, Louie!"
In the end after Morgana's defeat, Carlotta is seen celebrating along with the humans and merfolk by singing "Here on the Land and Sea". She then picks up Chef Louis and dances with him.
On Carlotta's original design cell (as revealed in the gallery below) her dress was originally green instead of maroon like we see in the final film and subsequent appearances.
Carlotta's maid outfit is exactly the same as Cinderella's, the only difference being the sleeves being form-fitting and with cuffs at the end.